The proposed investigations are aimed to examine the development and role of T-lymphocyte and antibody mediated immune response to respiratory syncytial virus infection in infancy and childhood. It is planned to examine the relationship of the respiratory mucosal immunity and T-lymphocyte mediated immunoregulatory mechanisms in the newborn infant to the nature of specific immune response and the severity of infection with respiratory syncytial virus. The studies will be carried out in newborn infants and hospitalized subjects with different clinical forms of respiratory syncytial virus infection, employing a variety of immunologic techniques.